1. Field of the Invention
The present invention relates to branched polycarbonates and a process for production thereof, and more particularly to novel branched polycarbonates having properties suitable for blow molding to produce large sized blow molded articles with less heterogeneity of thickness and to an efficient process for production thereof.
2. Description of the related arts
It has been difficult to produce blow moldings from known polycarbonates since they behave as Newtonian fluid in their molten state. For dissolution of this problems, some processes have been proposed in Japanese Patent Publication Nos. 17149/1969, 23918/1972, 11733/1985 and the like wherein the coexistence of a polyfunctional organic compound containing three or more functional groups such as phloroglucine, trimellitic acid, 1-(.alpha.-methyl-.alpha.-(4'-hydroxyphenyl)ethyl)-4-(.alpha.',.alpha.'-bi s(4"-hydroxyphenyl)ethyl) benzene as a branching agent imparts a branching property to said polycarbonates. The thermoplastic branched polycarbonate obtained by their processes presents non-Newtonina fluid properties in the molten state, and its blow moldability can be improved to some extent. However, the subsequent investigations showed that thus obtained branched polycarbonates are not practical for production of large sized blow molding because of their insufficient melt resistance. Accordingly, an attempt for improvement is disclosed in Japanese Patent Application Laid-Open No. 146920/1987.
However, when melt resistance (melt tension) sufficient to produce large sized blow molding is imparted to the polycarbonate according to the improved process, melt viscosity is simultaneously increased to prolong molding time, resulting in another drawback such as a delayed molding operation cycle.
Further, processes for production of polycarbonate using phloroglucine or trimellitic acid as a branching agent have heretofore been known, as disclosed in for example, Japanese Patent Publication Nos. 17149/1969, 11733/1985. However, these processes suffer from a disadvantage in that the use of these branching agents is apt to cause coloring owing to a trace quantity of unreacted matter.
Moreover, 1,1,1-tris(4-hydroxyphenyl)ethane is proposed to be used as a branching agent in Japanese Patent Application Laid-Open No. 45318/1984. However, the specification of U.S. Pat. No. 4,415,723 discloses the polymer obtained by using this branching agent is colored to pale yellowish green in Comparative Example A, and suggests to use a branching agent such as 1,1,2-tris(4-hydroxyphenyl)ethane; 1,1,2-tris(4-hydroxyphenyl)propane or the like. However, the process disclosed in the above U.S. Pat. No. 4,415,723 can not completely solve the problems of coloring.
When the polycarbonate is branched for blow molding, its impact resistance is known to decrease. Accordingly, branched polycarbonates with high impact resistance have been expected to be developed.